1. Field of the Invention:
This invention relates to motion picture cameras.
2. Description of the Prior Art:
The motion picture camera as well as the general-purpose camera has been required to meet demands not only for high imaging performance but also for reduction in bulk and weight so as to be convenient to the photographer in management, for increase in reliability in operating the camera.
To record image information on a film strip of long length in a series of still pictures, there is provided a film feed device for intermittently advancing the film past an image gate in combination with a shutter device arranged to be driven in synchronism with the film feed device in such a manner that one picture frame of the film is exposed as the shutter device is opened when the film feed device stops the film from advancement, and the exposure is blocked when the film is driven to advance. The film feed device and the shutter device operate with a common driving motor so long as a release device is actuated by a trigger device, the latter being arraged to be accessible from the outside of the camera housing. The methods of establishing the responsive relation between the trigger and release devices employed in the presently available motion picture cameras may be divided into two main categories: the first is to make use of a mechanical linkage responsive to the operation of the trigger device to be acted on the release device; and the second is to make use of an electromagnetic means electrically connected to the trigger device through switch means.
The disadvantages of the former are that the photographer is required to exert a very large force in assuring effective operation of the trigger device along with the release device by his finger on which a large proportion of his attention must be concentrated; further, it is impossible to make use of a wireless remote control, and, still further, the use of the mechanical linkage leads to an increase in the complexity of the associated mechanisms.
The latter method has overcome the aforesaid disadvantages, since there is provided the electromagnetic means for the release device which is electrically connected to the trigger device, and all that the trigger device has to do is to control the electrical power supply to the electromagnetic device. Therefore, the magnitude of force necessary to operate the trigger device is largely reduced to enable the photographer to save the load of his finger. The use of the electromagnetic means is advantageous in performing wireless remote control photography. Further, because of the lack of the mechanical linkage as in the former method, the design flexibility of the camera mechanisms is increased. The only problem arising in the employment of the latter method is how to reduce consumption of electrical energy of a battery which amounts to a far larger level than is expected. When the number of batteries necessary to be used at a time in the camera is increased, it is unavoidable to sacrifice the aforesaid demand for minimization of the size and weight of the camera. On this account, the latter method must be embodied by realizing a provision for permitting the electromagnetic means to operate with as low an electrical power supply as possible.
The foregoing discussion generally applies to the various types of motion picture cameras.
Of the presently available films for use with motion picture cameras, there are what is called "silent film" adapted to optically record picture information alone, and what is called "sound film" capable of recording not only picture information optically but also sound information magnetically.
One example of the round film is disclosed in U.S. Pat. No. 3,858,968 of Eastman Kodak Company and is sold from the same company under the trade name of "Sound Movie Film". This film has a track of magnetic recording material as applied on a film strip which is conventionally usable as a silent film along one side edge on the surface thereof and is accommodated in a cassette similar to the silent film, so that when the sound film is used, the photographer need only to load the cassette by itself into a chamber provided in the camera housing. Unlike the silent film cassette, however, the cassette for the sound film is designed to have not only a window as an exposure aperture but also a cutout or recess for sound recording station, the window and recess being spaced apart from each other but in a common film channel through which the sound film is passed from a supply spool to a take up spool mounted on a common shaft of the supply spool in the cassette housing.
For such sound film, there have been developed many sound motion picture cameras, as for example, shown in U.S. Pat. Nos. 3,771,864, 3,825,327, 3,880,504 and T920009 (Defensive Publication), and DOLS Nos. 2,254,664 and 2,417,095. The essential feature of these cameras is that there are provided what is lacked in any silent motion picture camera which is adapted for use with silent film known in the art from very old times, namely, a sound recording circuit device having a magnetic head for magnetic recording of sound information on the aforesaid sound track, and an additional film feed device adapted to transport the film at a substantially constant speed past the sound recording station, while the film is intermittently advanced past the picture taking station.
The second film feed device for continuously transporting the film at a substantially constant speed with reference to the magnetic head is generally constructed to include a capstan arranged to be driven for rotation at a constant speed and a pinch roller arranged upon actuation of a suitable member to press the film against the capstan in a resilient manner. For this purpose, while the capstan is usually made of solid material such as metal, the pinch roller is formed to an elastic ring by use of rubber, for example, and this ring is mounted to surround a metal core. This construction of the second film feed device assures the constant speed of transportation of the film with the help of the elastic ring.
Since the pinch roller of such construction is susceptible of plastic deformation, it is required to move the pinch roller away from the capstan whenever the capstan is stopped, or otherwise the so-deformed ring of the pinch roller would give bad influence to the sound recording. Therefore, all the sound motion picture cameras and also the audio instruments having at least a capstan and a pinch roller for transportation of a film or tape have a provision for controlling the film or tape feed device of the capstan and pinch roller in such a manner that only when the film or tape is transported, the pinch roller is allowed in resilient contact with the capstan. In this manner, the pinch roller is prevented from being deformed by the pressure which would be otherwise effected when the pinch roller is left in resilient contact with the capstan after the capstan is stopped. The creation of a gap between the capstan and the pinch roller when not in use provides an additional advantage of making the loading operation of the cassette easier.
It is known to provide many methods of selectively controlling the position of the pinch roller relative to the capstan, as, for example, disclosed in U.S. Pat. No. 3,880,504, wherein a shifting device for the pinch roller is mechanically linked to the trigger device. This arrangement gives rise to a problem that the photographer's finger acting on the trigger device cannot endure the stress for a longer time than when the trigger device is associated with the aforesaid release device along. Particularly with the sound motion picture camera, when the photographer's finger is tired so as not to exert a sufficient force in depressing the trigger device, the pressure of the pinch roller against the capstan varies to so large an extent that it is impossible to maintain the speed of transportation of the film at a constant level.
One proposal for solving this problem is disclosed in DOLS No. 2,417,095, wherein the shifting device is provided with electromagnetic means though it is uncertain whether or not this electromagnet means is utilized to actuate the release device, as arranged to cooperate with the trigger device through a switch for controlling electrical power supply to the electromagnetic means. By the use of this electromagnetic means, the picture and sound recording characteristics of the camera is stabilized against the variation of force of the photographer's finger on the trigger device, since the engagement of the pinch roller with the capstan is established with an always constant pressure.
The mere combination of DOLS No. 2,417,095 with the known method of application of electromagnetic means to the release device, that is, the fact that the shifting and release devices are actuated by separate electromagnetic means, however, will lead to an increase in the amount of consumption of electrical energy to effect an equivalent result of picture and sound recording. As has been mentioned above, the intensity of current necessary to assure the effective operation of each electromagnetic means is comparatively large, so that there is need for the camera to accommodate a number of additional batteries for the additional electromagnetic means. This calls for a large increase in the bulk and weight of the motion picture camera.